Cadence sensing and torque sensing

Cadence

A magnet on the crank and a pickup on the frame count rotations. Cross a threshold and the motor applies the assist level you selected. Bafang’s BBS02 and BBSHD are the cadence mid-drives most workshops already know. The feel can be a step: nothing, then the chosen level. Ramps in the controller soften that step. They do not turn the sensor into a torque sensor.

Torque

A torque sensor measures force in the spindle, the bracket or the dropout. Assist follows your effort, so a light spin gets a little help and a standing start gets more. Tongsheng’s TSDZ2B, CYC’s Photon motors and Pendix’s eDrive are torque systems on this catalogue. They tend to feel like a stronger rider. They also put the sensor in the load path, so the spindle and the controller are one spare, not two.

Combined, and the ones that are neither

Some mid-drives read both cadence and torque. The card says combined when that is what the maker published. Friction drives and trailers often use a simpler switch or a throttle. Do not promote them to torque sensing because the ride felt smooth.

• Cadence: cheaper sensors, more programming, a clearer on/off.
• Torque: proportional help, more natural on a shared path, usually more money.
• A throttle plus a cadence sensor is a third behaviour. It is its own legal question.
• The sensor lead is part of the install. A crushed pickup is the first thing to check when assist vanishes.